Surface energetics and adhesion

Tn recent years, developing interests in surface energetics and adhesion of liquid-like polymers, or polymer liquids, have prompted both theoretical and experimental work on surface tension. Unlike low molecular weight liquids, polymer liquids have not been extensively studied. Bondi and Simkin (1) mentioned surface tension in their study on high molecular weight liquids. Roe (28) applied both the cell theory of polymer liquids and the hole theory of surface tension of simple liquids to develop an approximate theory of surface tensions of polymer liquids. His approach has met some degree of success. Notably, both Bondi s and Roes work are somewhat related to the cell theory introduced by Prigogine and... 

Surface Energetics and Wettability Theory. The surface energetics and wettability theory of adhesion is concerned with the effect of intermolecular and interatomic forces on the surface energies of the adhesive and the adherend and the interfacial energy between the two. 

We develop certain aspects of the adsorption theory of adhesion more fully than has been done previously, based solely on (free) surface energetics, and show how they can be applied to real or practical systems. As a consequence, it is shown that the deBruyne adhesion rule [7] is incorrect in part. Our concern is mainly with what we believe to be the most important problem in the making of adhesive bonds—that is, the achievement of extensive and proper (no intermediate phase) interfacial contact. We discuss also the breaking strength of certain adhesive joints where this is necessary to the development of our thesis. However, the processes of making and breaking adhesive joints bear no... 

Baler, R.E. and Meyer, A.E., "Surface Energetics and Biological Adhesion," Proceedings, International Symposium on Physlochemical Aspects of Polymer Surfaces (K. L. Mittal, ed.) Plenum Press, NY, 1982. 

Several papers by Kendall treated the subject of adhesion rather explicitly with simple models of mechanics. Andrews and Kinloch attempted to separate "adhesion" and "adhesive joint strength" and established that the intrinsic failure energy is close to the work of adhesion when pure interfacial failure occurs. Kloubek attributed the interaction of polar forces to the contribution of the work of adhesion. The effect of surface energetics and wetting on adhesion has been summarized by Kaelble, Mittal, and Zisman . ... 

Over the past several decades, much study has been focused on surface energetics, wetting, adhesion, etc., and some generalizations have been developed. These can be useful guides to the adhesive selection and surface preparation needed to form reliable, strong adhesive bonds. Only a brief exposure to some of this valuable information can be presented here, but further reading is available in Chapter 3 and other chapters of this Handbook, and in listed references. 

Given the importance of surface and interfacial energies in determining the interfacial adhesion between materials, and the unreliability of the contact angle methods to predict the surface energetics of solids, it has become necessary to develop a new class of theoretical and experimental tools to measure the surface and interfacial energetics of solids. Thia new class of methods is based on the recent developments in the theories of contact mechanics, particularly the JKR theory. 

The characteristics of particulate filled polymers are determined by the properties of their components, composition, structure and interactions [2]. These four factors are equally important and their effects are interconnected. The specific surface area of the filler, for example, determines the size of the contact surface between the filler and the polymer, thus the amount of the interphase formed. Surface energetics influence structure, and also the effect of composition on properties, as well as the mode of deformation. A relevant discussion of adhesion and interaction in particulate filled polymers cannot be carried out without defining the role of all factors which influence the properties of the composite and the interrelation among them. 

Although a number of filler characteristics influence composite properties, particle size, specific surface area, and surface energetics must again be mentioned here. All three also influence interfacial interactions. In the case of large particles and weak adhesion, the separation of the matrix/ filler interface is easy, debonding takes place under the effect of a small external load. Small particles form aggregates which cause a deterioration in the mechanical properties of the composites. Specific surface area, which depends on the particle size distribution of the filler, determines the size of the contact surface between the polymer and the filler. The size of this surface plays a crucial role in interfacial interactions and the formation of the interphase. 

The interphase is the volume of material in which the properties of one substance gradually change into the propeities of another. The intetphase is useful for describing the properties of an adhesive bond. The interface, contained within the interphase, is the plane of contact between the surface of one material and the surface of another. F.xcepl in certain special cases, the interface is imaginary. It is useful in describing surface energetics. 

The mechanism of electrodeposition or electrocrystallization28 29 involves, as a first step, the reduction of a cation on the substrate surface (aided by an applied potential or current) to form an adatom, and its migration over the surface to an energetically favourable site. Other atoms of the electrodeposit aggregate with the first, forming the nucleus of a new phase. The nucleus grows parallel and/or perpendicular to the surface. Clearly, a number of nuclei can form and grow on the surface. When all the electrode surface is covered with at least a monolayer, deposition is on the same metal rather than on a different metal substrate. As is to be expected, the formation of the first layers determines the structure and adhesion of the electrodeposit. 

Schonhorn, H., and Sharpe, L., Surface Energetics, Adhesion, and Adhesive Joints II, Journal of Polymer Science PartB Polymer Letters, vol. 2, no. 7, 1964, p. 719. 

---